The present invention relates to spectroscopic sensors and, more specifically, to on-chip spectroscopic sensors with optical fringe suppression.
Natural gas is an important part of global energy generation. However, as natural gas is collected from wells and carried along pipes, there is a risk that methane may leak. Spectroscopic sensors may therefore be used to detect the presence of fugitive methane. While traditional spectroscopic sensors may be large, expensive and delicate, on-chip spectroscopic sensors have been developed.
On-chip spectroscopic sensors may utilize laser absorption spectroscopy (LAS) to determine an atomic and/or molecular composition of matter by analyzing the frequency properties of laser light passing through an analyte. However, as the laser light of various frequencies passes through the on-chip spectroscopic sensors, reflections of light from unwanted interfaces may lead to various standing wave interference patterns, which, if not properly accounted for, may lead to imprecise spectroscopy as the signal may appear to include oscillations. This effect may be known as optical fringing, or etaloning, as it is caused by the light circulating within an optical cavity, which is an etalon. The use of silicon photonic waveguides within the on-chip spectroscopic sensors may be particularly prone to optical fringes with difficult to predict patterns, owing to its relatively large thermo-optic coefficient.